<ion-header>
  <ion-toolbar>
    <ion-buttons slot="start" (click)="gotohome()">
      <ion-icon name="arrow-back"></ion-icon>
    </ion-buttons>
    <ion-title>popover</ion-title>
    <ion-buttons slot="end" (click)="presentPopover($event)">
      <ion-icon size="large" name="contact"></ion-icon>
    </ion-buttons>
  </ion-toolbar>
</ion-header>

<ion-content padding>
    (提示：事件函数参数加上$event可在点击时展示在元素附近，否则是垂直居中显示)
</ion-content>
